I got some weed that I dried too long. It quite easily breaks compared to usual. Is it possible to make it a bit better? Can I spray water on it? Or can I put something with it in the containement? Or is it too late already?
But I shouldn’t mess it up and make it mold after e.g. too much water 
Welcome back. If it’s for curing your SOL. If you just want it to be a little more moist add some broveda (spelling) packs or like in the old high school days some citrus peels.
Try a fresh pot leaf, or a piece of orange rind, etc. and place in the jar with a hygrometer to keep from introducing too much moisture.
If its horrible and harsh i have managed to rescue some bud that was destined for the compost by doing a water cure but id try using a leaf or orange peel like the others are suggesting. Most peelings or skins work because they contain moisture but they can also impart a bit of themselves into the taste and flavour.
Edit:
Before doing a water cure just make sure to read up on what actually happens and how it effects your buds because it can and probably will effect taste and smell and even the strength.
Place on brownie baking tray, spread out the buds. Take a spray bottle on mist setting and give it about 4 or 5 sprays about a ft away, cover for about 20 min for the buds to soak up moisture , remove the cover and leave open for about 10 min to allow standing water dropplets to dry and throw into a jar, burp for 2 days once a day and that should make em tolerable again, throwing in a boveda or Integra pack should maintain it for ya, dry climates I suggest the 62 and moist environment go with 58
If it’s that dry, another option is to make edibles / oil / tincture from it. At least that way it doesn’t go to waste.
weed in a zip lock, open the zip lock, dip a couple of fingers in water, and flick a few drops on the side of the bag. Close the bag almost all the way, breathe air into the small opening, a few hot breaths eventually leaving the bag fluffy full of humid /breath/air. close the rest of the way. leave overnight, occasionally roll the weed in the bag around, and flick off any trim stuck to the side. try to separate the trim before actually best with just bud. use just a few drops it will stretch and it is an even hydrate from bud to stem. Clouding got to get a humid cloud in there.
I have found that rehydration my over dried nuggs causes them to be rubbery and lowers their potency quite a bit. I would not rehydrate the nuggs, I would separate them into smaller containers so that I could keep most of it jarred and only have a small amount opened at any time… then try to make sure my next batch does not over dry.
I’m with @MrWizard
Pick a fresh pot leaf and put it in with you dried stuff. I have had success with this.
That reminds me of another good option. Keep the over-dried nugs segregated, and then mix 1:1 or any other ratio with normal nugs. That should balance it out.
Imo once its toast . Its toast . Only option is finish decarbing and eat it . Or concentrates.
I guess it would depend if it was fresh and dried too quick . Or just not sealed right and was found dry.
The latter rso , if dried too quick qwiso.
Rso involves soaking in iso alcohol produces green dark full spectrum oil . Qwiso is quick wash frozen and will produce a nice looking /tasting product if done right .
An old growers trick from back in the day folks…been doing this for over 25+ yrs.
If there’s any moisture even deep down in the big stems . I’ve had luck sealing it for a few weeks . Like loose vac seal , or 5g bucket with gamma lid or just tape the lid so its 100% sealed and forget about it.
If you don’t want your pot to smell like citrus, instead of putting orange peel in the ziplock bag with it, try a piece of bread.
However, depending on how much you have, the brownies idea is great! I used a Levo machine to make my over-dry stash into infused coconut oil and the brownies were delicious!
It’ll never be the same once it’s dried out. It’ll still be fine though.
Bovedas work, leaves work, sealed climate controlled chambers works…